Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2002-11-21
2004-03-23
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S901000
Reexamination Certificate
active
06709160
ABSTRACT:
FIELD OF THE INVENTION
The present relates to turbochargers for internal combustion engines and more particularly to a simplified assembly of and arrangement for lubricating the bearing system of a turbocharger.
BACKGROUND OF THE INVENTION
Turbochargers are widely used on internal combustion engines, and in the past have been particularly used with large diesel engines, especially for highway trucks and marine applications. In distinction to superchargers, which derive their power directly from the crankshaft of the engine, turbochargers are driven by the engine exhaust gases. Exhaust gases are directed to and drive a turbine, and the turbine shaft is connected to and drives the compressor. Ambient air is compressed by the compressor and fed into the intake manifold of the engine.
More recently, in addition to use in connection with large diesel engines, turbochargers have become popular for use in connection with smaller, passenger car power plants. The use of a turbocharger in passenger car applications permits selection of a power plant that develops the same amount of horsepower from a smaller, lower mass engine. Using a lower mass engine has the desired effect of decreasing the overall weight of the car, increasing sporty performance, and enhancing fuel economy. Moreover, use of a turbocharger permits more complete combustion of the fuel delivered to the engine, thereby reducing the hydrocarbon emissions of the engine which contributes to the highly desirable goal of a cleaner environment.
As the use of turbochargers finds greater acceptance in passenger car applications, three design criteria have moved to the forefront. First, the market is demanding that all components of the power plant of a passenger car, including the turbocharger, must provide reliable operation for a much longer period than was demanded in the past. That is, while it may have been acceptable in the past to require a major engine overhaul after 80,000-100,000 miles, it is now necessary to design engine components for reliable operation in excess of 200,000 miles of operation. This means that extra care must be taken to ensure proper lubrication of bearings supporting devices that rotate at very high rotational speeds, as in a turbocharger.
The second design criterion that has moved to the forefront in passenger car applications is that the power plant must meet or exceed very strict requirements in the area of minimized hydrocarbon emissions. Third, with the mass production of turbochargers for smaller passenger cars, it is highly desirable to design a turbocharger that meets the above criteria and is comprised of a minimum number of parts, which parts are easy to manufacture and easy to assemble, in order to provide a cost effective and reliable turbocharger.
As stated above, the demand for engine components that provide an extended service life requires that extra care must be taken to ensure proper lubrication of bearings that support devices rotating at very high rotational speeds, as in a turbocharger. In the prior art, two basic systems have been adopted to deliver lubricating oil to the critical wear points of a turbocharger using two floating journal bearings. First, the central bearing housing can be provided with lubricating oil channels directed to the top of the journal bearings, the so-called “top-delivered” system. With this system, oil is delivered to the top of the journal bearings, usually at the axial center of the bearings, and the bearings are normally provided with radial apertures in the center of the bearing to allow flow of the lubricating oil radially inwardly to the interface between the shaft and the inside diameter of the journal bearing. In this system, the oil must be supplied at high pressure in order to ensure that it will migrate inwardly through an aperture in a journal bearing while the journal bearing is spinning at a very high rate.
The second basic system for delivering lubricating oil to the journal bearings of a turbocharger is to deliver the oil to the center of the rotating shaft and allow the oil to migrate axially outwardly along the shaft and over the bearings before being released to the oil return sump and to the engine crankcase. In both of these systems, in order to provide adequate lubrication to the bearings, a high flow rate of oil has been provided to ensure that adequate coverage of the bearing surfaces is obtained. Especially in connection with the top-delivered system, a high percentage of the oil flowing through the system contacts only the outboard half of the outside diameter of the journal bearing before being expelled into the oil return sump. This means that a very high volume of flow must be provided to obtain any oil film coverage of the other surfaces of the journal bearing.
This high flow of oil through the bearing housing of a turbocharger increases the opportunity for oil to leak from the bearing housing into the turbine or compressor portions of the turbocharger. Internal combustion engines, whether diesel or gasoline, are designed for optimum combustion of the fuel for which they are designed. In either type of engine, when engine crankcase lubricating oil is introduced into the combustion chamber of the engine, it is not burned effectively, and a large portion of that oil is emitted as an undesired hydrocarbon pollutant. Engine manufacturers have been diligent in reducing the amount of lubricating oil that is allowed to enter the combustion chamber of the engine by improving piston ring and valve stem seal designs, and the like. Unfortunately, turbocharger design has not kept pace with this trend.
As stated, turbochargers commonly use crankcase oil to lubricate the rotating bearing interfaces as well as the thrust surfaces that limit axial excursions of the shaft and its turbine and compressor wheels. Since turbochargers operate at extremely high rotational speeds, sometimes in excess of 200,000 RPM, generous lubrication of these bearing surfaces is critical in order to provide a turbocharger capable of a long and reliable service life. With this high flow rate of oil over the journal bearings comes the possibility that some percentage of the oil will escape past the barriers set up in the turbocharger to prevent lubricating oil from entering either the turbine housing or the compressor housing.
More specifically, if lubricating oil from the center bearing housing migrates beyond the piston ring seal provided to prevent such migration at the turbine end of the housing, lubricating oil will enter the turbine housing and will be expelled with the exhaust flow out of the engine into the atmosphere. On the other hand, if lubricating oil from the center bearing housing migrates beyond the piston ring seal at the compressor end of the housing, the lubricating oil will enter the compressor housing and will be injected into the combustion chamber of the engine where it will not be properly burned and will be emitted by the engine as an undesired hydrocarbon pollutant. Unfortunately, as a result of this phenomenon, it is commonly believed that over half of the hydrocarbon emissions of turbocharged engines come from oil leakage through the turbocharger, not from the engine itself.
Thus, it seems that these two design criteria point a designer in different directions. That is, if it is desired to achieve longer service life of a turbocharger, the flow of oil over the bearings should be increased to minimize metal-to-metal contact between parts and decrease wear of the parts. On the other hand, if hydrocarbon emissions of the engine are to be decreased, oil flow through the bearing housing should be minimized to decrease the opportunity for oil leakage into the turbine or compressor housings of the turbocharger.
Many attempts have been made to minimize leakage of oil from a turbocharger bearing housing, but these have always taken the form of adding a number of parts or a new sub-assembly, such as an oil deflector, extra seals, or the like. While this may assist in reducing oil leakage from the bearing housing, it is contrary to the third
Gray, III Allen W.
Hall Richard D.
Kierat Jaroslaw M.
Ward Daniel N.
Borg-Warner Inc.
Dziegielewski Greg
Footland Lenard A.
Pendorf & Cutliff
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